1. Field of the Invention
This invention relates to a method and apparatus for performing a recording/reproduction of an information on/from a recording medium having recording tracks each defined by wobbled grooves.
2. Description of the Related Art
Nowadays, a need of a larger capacity has been increased in an optical recording/reproducing field or an opto-magnetic recording/reproducing field. Accordingly, in a recording medium such as a DVD-RAM (digital versatile disc-random access memory) and so on, there has been suggested a so-called land/groove recording system having an information recorded on both of land and groove tracks.
For example, a DVD-RAM as shown in FIG. 1 is provided with wobbled groove tracks 10 and land tracks wobbled alternately with the groove tracks 10 in the width direction of the groove tracks 10. The groove and land tracks 10 and 12 are used as recording regions. A certain period of wobbling signals are included in a wobbled portion 14 of each of the groove and land tracks 10 and 12, hereinafter referred to as "wobbled part", that is, in each side of the land and groove tracks 10 and 12. A recording/reproducing apparatus for an optical recording medium generates a rotation control information about the DVD-RAM and a recording clock with the aid of the wobbling signals. Also, each of the land and groove tracks 10 and 12 is alternated with a identification (ID) region consisting of a pre-pit train 16. The pre-pit train 16 includes an address information for indicating the physical position of the groove and land tracks 10 and 12. The physical positions of all the groove and land tracks 10 and 12 are indicated with such ID regions, thereby recording an information on all the groove and land tracks 10 and 12. As a result, a large amount of information can be recorded in the DVD-RAM.
In the optical recording medium of such a land/groove recording system, wobbling signals detected from each of the adjacent groove and land tracks 10 and 12 have a contrary phase to each other. This is caused by a physical shape and an optical characteristic in the groove and land tracks 10 and 12. Thus, when a laser light beam is transferred from the groove track 10 to the land track 12 or vice versa, a phase of the wobbling signal is inverted. For example, in a single-spiral type of recording medium, the wobbled groove and land tracks 10 and 12 are alternated every once rotation, so that a phase of the wobbling signal is inverted whenever the recording medium is rotated once. More specifically, an electrical signal as shown in FIG. 2A is detected from the groove track 10 while an electrical signal as shown in FIG. 2B is detected from the land track 12. Referring to FIGS. 2A and 2B, it is to be noted that first and second wobbling signal 13A and 13B detected from the groove track 10 are phases contrary to third and fourth wobbling signals 13C and 13D detected from the land track 12, respectively. When a light beam enters the land track 12 from the groove track 10, the fourth wobbling signal 13D in FIG. 2B having a phase contrary to the first wobbling signal 13A in FIG. 2A emerges at the rear portion of the first wobbling signal 13A. On the other hand, when a light beam enters the groove track 12 from the land track 12, the second wobbling signal 13B in FIG. 2A having a phase contrary to the third wobbling signal 13C in FIG. 2B emerges at the rear portion of the third wobbling signal 13C. In other words, in the single-spiral type of optical recording medium, the land and groove tracks are alternated or replaced every once rotation, so that a phase of the wobbling signal becomes inconsistent at their crossing position.
Meanwhile, a general recording clock is generated by slicing the wobbling signal 13 into a zero-crossing level to generate a wobbling pulse signal having a rectangular wave shape and then applying the wobbling pulse signal to a phase synchronizing loop. The recording clock generated in this manner has a different phase whenever a light beam is transferred from the groove track 10 to the land tracks 12 or vice versa. This results from a phase of the wobbling signal being inverted whenever a light beam is transferred from the groove track 10 to the land track 12 or vice versa. A rotation control information produced based on the recording clock also becomes different whenever a light beam is transferred from the groove track 10 to the land track 12 or vice versa. Accordingly, a recording/reproducing apparatus for the optical recording medium must invert the polarity of the wobbling signal each time a light beam is transferred from the groove track 10 to the land track 12 or vice versa so as to perform the generation of recording clock and the rotation control accurately.
In order to switch the polarity of the wobbling signal, the recording/reproducing apparatus must accurately identify whether a track being currently driven (i.e., recorded or reproduced) is a land track or a groove track. If such a land/groove identification is accurately performed, then it is impossible for the recording/reproducing apparatus to do the clock generation and the rotation control smoothly. In addition, a tracking control of push-pull system also requires the land/groove identification. This results from the polarity of the tracking error signal being inverted each time a light beam is transferred from the groove track to the land track or vice versa. Likewise, when the land/groove identification is accurately performed, the tracking control of push-pull system also is not done smoothly.
The above-mentioned land/groove identification is usually dependent upon a push-pull signal detected from the identification (ID) region. However, the push-pull signal may be not at all detected or may be inaccurately detected from the optical recording medium. For example, since a header region is not read in the case of performing an additional operation such as a track search and so on, the push-pull signal is not at all detected. Further, the push-pull signal is not detected accurately in the case of having a large tracking offset. It becomes difficult to do the land/groove identification when the push-pull signal at the header region as mentioned above is not detected accurately.